1. Field of the Invention
This invention relates to radial seals such as tip seals employed in rotating turbine machinery and disposed between stationary and rotating parts.
2. Description of the Prior Art
Radial seals can become deteriorated due to the presence of particulate material that enters the turbine and is flung into the area containing the tip seals where it cannot escape, then batters and erodes the tip seals, bucket covers and adjacent stationary parts.
A persistent and costly problem for steam and gas turbines using radial tip seals to minimize leakage over the shrouds or bucket covers of the turbine stages is the damage caused by particles. The particles can be either broken pieces of the turbine or foreign particles that enter the turbine with the steam. These particles, once having reached the location of the tip seals, have great difficulty escaping and are generally forced to circulate at great speed, causing damage to the seals, bucket covers and tenons.
Means is shown in my U.S. Pat. No. 5,271,712, utilizing a small circumferential opening in the tip seal in conjunction with a scoop to encourage the particles to be discharged from the tip seal area by deflecting them through the small opening. The scoop of U.S. Pat. No. 5,271,721 is an integral part of the tip seal. Consequently, it is limited in application to those tip seals with sufficient mass and strength to hold the scoop in place in spite of particle impacts and large, time varying steam forces.
The scoop, being integral with the tip seal must generally be made of the same material as the tip seal. This is often a handicap since the tip seal material is selected to be capable of rubbing away with a minimum of damage to adjacent rotating parts such as the bucket covers. The scoop, on the other hand, should ideally be made of material resistant to erosion and impact loads.